Let's see.
Kobo Touch, Kobo Mini, Kobo Aura One, Kobo Glo HD, Kobo Clara HD, Kindle Touch, Kindle Paperwhite 2, Kindle Paperwhite 3, Kindle Oasis 2 and Cervantes BQ. Also a Fire HD 8 tablet and a Pixel 3 phone.
So that's 12 reading devices, 10 eink ereaders.
Why do I keep them?
Well I got rid of my first, a Kindle 2i and always regretted it. Because I think it would have been nice to still have my original ereader. I'm also sentimental about my Mini because it's a reader I really like and you can't really get 5" readers any more.
I have gotten rid of a few ereaders but I'm at the point where most of my family don't want cast offs any more

and you don't really get much for them second hand. They don't take up much space and I can allocate them for different purposes. I have one that stays in my work desk drawer, one that I carry in my backpack, a PW downstairs and one in the bedroom and so on.
I do try to resist buying
every new model but sometimes I am tempted.
So I just shrug and call myself a collector